In a typical mobile communications environment, a user equipment (UE) device such as a mobile phone (also known as a cellular or cell phone), a laptop computer with wireless communications capability, or a personal digital assistant (PDA), may communicate voice and/or data signals with one or more service networks. The wireless communications between the UE and the service networks may be in compliance with various wireless technologies. A long-term evolution (LTE) system, initiated by the third generation partnership project (3GPP), is now being regarded as a new radio interface and radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. An evolution of core network with non-radio access aspects, known as System Architecture Evolution (SAE), is also initiated by 3GPP in accompanying with LTE.
Evolved Packet System (EPS) is a purely IP based network, consisting of user equipments (UEs), a LTE radio access network known as Evolved Universal Terrestrial Radio Access Network (E-UTRAN), and a SAE core network known as Evolved Packet Core (EPC). The EPS uses the concept of “EPS hearers” to route IP traffic from a gateway in external packet data networks to the UE. A bearer is an IP packet flow with a specific Quality of Service (QoS) between the gateway and the UE. The E-UTRAN is simply a network of plurality of evolved Node-Bs (eNBs) communicating with a plurality of UEs, which generate a flat architecture and there is no centralized controller. The eNBs are normally inter-connected via the X2-interface and towards the EPC by the S1-interface. The EPC includes a mobility management entity (MME), a Home Subscriber Server (HSS), a serving gateway (SGW), a packet data network gateway (PDN GW or PGW). The MME deals with the control plane. It handles the signalling related to mobility and security for E-UTRAN access. The MME is responsible for the tracking and the paging of UE in idle-mode. It is the termination point of the Non-Access Stratum (NAS). The MME handles bearer management and connection management. The HSS is a database that contains user-related and subscriber-related information. The HSS also provides support functions in mobility management, call and session setup, user authentication and access authorization. The Serving GW is the point of interconnect between the radio-side and the EPC, and it serves the UE by routing the incoming and outgoing IP packets. The PDN GW is the point of interconnect between the EPC and external IP networks called PDN (Packet Data Network), and it routes packets to and from the PDNs.
A long term evolution-advanced (UE-A) system, as its name implies, is an evolution of the UE system and has a similar network structure to the UE system.
In LTE-related systems, Proximity-based Service (ProSe) communication has been developed as a technology which allows UEs to communicate directly with each other in close proximity without transmitting/receiving data and/or control signals to the other via an eNB, which means a local or direct path can be used between the UEs. Therefore, in the 3GPP UE spectrum, the operator can move the data path (i.e., user plane) off the access to core networks to direct links between the UEs.
To extend the communication range for the public safety, a public safety ProSe UE capable of using a relay function can be configured to act as a relay UE, either UE-to-UE relay or a UE-to-Network relay. When being the relay UE, the relay UE may consume extra power for a relay discovery procedure and relay communication. Due to the limited battery life, a relay discovery procedure of the relay UE should be activated only when needed. However it is still not clear when and how the relay UE and a UE which requiring a relay perform the relay discovery procedure and activates the relay function.
As a result, methods of relay discovery and communication that may solve these problems are required.